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What's more efficient, storage / direct feed

Discussion in 'Alternative Energy' started by Jules_Theone, Apr 21, 2009.

  1. Jules_Theone

    Jules_Theone Member

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    I am wondering which system would be most efficient, or perhaps an alternative idea?

    1. 60 x 15Ah lead acid batteries connected to two 20watt solar panels which charge up through a 12Amp solar charge regulator. When the regulator says the battery pack is full, I run my PC, monitor, router etc from the batteries with a 600watt inverter until the regulator says the batteries have approx a third charge left. Then connect the PC etc to the mains again and allow the solar panels to charge up the batteries again. The ratio of power to charging time I have found with this is approx 12 hours:2 weeks.

    2. Build a grid tie inverter like I've done before, but improved by tcmtech's recommendations, which feeds the <40watts directly into the grid (which should offset the power being used to power the PC etc).

    I am also working on a simple exercise bike generator to add to the power from the solar panels.

    Feel free to punch holes in these idea...
     
  2. ericgibbs

    ericgibbs Well-Known Member Most Helpful Member

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    hi Jules,
    Is this a serious question or are you just pulling our legs....:D
     
  3. Sceadwian

    Sceadwian Banned

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    Wait, am I reading this right, 60 15AH lead acid batteries? What a mess that'd be, just managing the charge conditions would be a nightmare and probably fail catastrophically at some point. It would have to be more efficient to use a grid tie system.
     
  4. dave

    Dave New Member

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  5. Jules_Theone

    Jules_Theone Member

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    Well, I've set up the battery pack / inverter idea already because I've got all the bits, but is there a better way so I don't have to keep swapping things round, unplugging my PC all the time, perhaps a more automated system?
     
  6. ericgibbs

    ericgibbs Well-Known Member Most Helpful Member

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    hi,
    The two 20Watt PV's will only give about 3amps total on the sunniest day [100% eff].
    Even thought its a 12A solar charge regulator, you will only get about 3A charge at max PV output.

    The 60 *15Ahr batteries, thats 900AHr

    The sums dont come out right for charging a 900AHr pack from a 40W PV.:)
     
    Last edited: Apr 21, 2009
  7. Sceadwian

    Sceadwian Banned

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    Not to mention the relative absurdity of putting that many lead acid cells in parallel... The pulse current that would put out if you dead shorted the power leads on accident would be incredible. WAY past explosive vaporization of metal.
     
  8. Jules_Theone

    Jules_Theone Member

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    Doesn't it just take a VERY long time to charge up? I don't run the batteries down to nothing because I've had trouble charging such a large battery pack when it's completely flat. The solar panels don't charge it, and it discharges more than the panels can charge. I've had one bunch of batteries go down to 0.8v before I realised, obviously they was written off at that point (high resistance).

    Are you saying that the solar panels aren't big enough for such a large battery pack? That's why i was thinking of adding other sources of charge.
     
  9. Jules_Theone

    Jules_Theone Member

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    Sceadwian, I haven't done THAT yet... I've put a single strand of copper cable (1mm dia?) for a fuse on the largest pack and 20A fuses on the others. Here's the pics of the setup. The positive and negative sides of the big pack are the bare copper screwed on the left and right of the batteries. and the inverter is above the batteries.
     

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  10. ericgibbs

    ericgibbs Well-Known Member Most Helpful Member

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    hi,
    Even at 3A charge from the PV and a 900AHr pack thats 300 hours of maximum output.

    Even at 8 hours of brilliant sunshine for 8 hours/day thats 37.5Days.!

    At 50% that becomes 75 days and for 4 hours Sun per day thats 150 days..

    The UK 'summer' dosnt last that long... you see the point Im making.:)
     
  11. Sceadwian

    Sceadwian Banned

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    Keep in mind lead acid batteries self discharge pretty badly, and 60 in parallel will have bad voltage imbalance between cells causing even more wasted current, efficiency would go right out the window. A straight grid tie and the meter stops spinning just that much right then.
     
  12. Jules_Theone

    Jules_Theone Member

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    Yeah, the math doesn't work because the batteries cannot all be charged at the same time as they discharge faster than they will charge, I have several battery packs that I connect in and out, and charge some with a car battery charger (which isn't the idea!).

    I think I will need more solar panels or another source to keep the packs charged up.
     
    Last edited: Apr 21, 2009
  13. Sceadwian

    Sceadwian Banned

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    So I don't think there's really any question here =) Grid tie is the only way to go.
     
  14. Jules_Theone

    Jules_Theone Member

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    Ok, but does the 'generator' need to be bigger to make it worth doing because I thought that the more power going in, the more efficient it will be?
     
  15. Sceadwian

    Sceadwian Banned

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    Well if you don't generate a lot of power in the first place the entire project is pointless, for the 40 watts your solar cell is generating even assuming it runs 100% efficient all the time, all you have to do replace one incandescent bulb with a CFL bulbs to save MORE power than the entire project will create. The gain is not just negligible the complexity of the system involved makes it worse than if you just left it alone.
     
  16. tcmtech

    tcmtech Well-Known Member Most Helpful Member

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    The whole point of the grid tie design was to get rid of all of the expense and hassle of big battery banks and independent inverters plus having to switch back and forth all of the time.
    Plus when you factor in the actual efficiency losses of any battery as a energy input Vs usable energy output your taking even more power before you get anything back.

    Also A properly designed GTI is basically maintenance free! When there is sufficient input power it does its job. Plus everything in the house gets a little bit of a power savings from it!

    Given what you are using for solar panels a GTI is the most logical way to go.
    The net efficiency gain is going to be far greater and the ease of use is basically "plug and play".
    And again if built right a GTI should run for decades without giving you any problems and has almost no maintenance requirenments.
    Plus a little forward thinking durring the GTI build should allow you to have added capabilities with it later on. Like wider operating voltage and power handling abilities!

    I have never seen a battery based system that could do that!
     

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